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API Reference
=============

Operators
---------
Operators allow for generation of certain types of tasks that become nodes in
the DAG when instantiated. All operators derive from :class:`~airflow.models.BaseOperator` and
inherit many attributes and methods that way.

There are 3 main types of operators:

- Operators that performs an **action**, or tell another system to
  perform an action
- **Transfer** operators move data from one system to another
- **Sensors** are a certain type of operator that will keep running until a
  certain criterion is met. Examples include a specific file landing in HDFS or
  S3, a partition appearing in Hive, or a specific time of the day. Sensors
  are derived from :class:`~airflow.sensors.base_sensor_operator.BaseSensorOperator` and run a poke
  method at a specified :attr:`~airflow.sensors.base_sensor_operator.BaseSensorOperator.poke_interval` until it returns ``True``.

BaseOperator
''''''''''''
All operators are derived from :class:`~airflow.models.BaseOperator` and acquire much
functionality through inheritance. Since this is the core of the engine,
it's worth taking the time to understand the parameters of :class:`~airflow.models.BaseOperator`
to understand the primitive features that can be leveraged in your
DAGs.

BaseSensorOperator
''''''''''''''''''
All sensors are derived from :class:`~airflow.sensors.base_sensor_operator.BaseSensorOperator`. All sensors inherit
the :attr:`~airflow.sensors.base_sensor_operator.BaseSensorOperator.timeout` and :attr:`~airflow.sensors.base_sensor_operator.BaseSensorOperator.poke_interval` on top of the :class:`~airflow.models.BaseOperator`
attributes.

Operators packages
''''''''''''''''''
All operators are in the following packages:

.. toctree::
  :includehidden:
  :glob:
  :maxdepth: 1

  airflow/operators/index

  airflow/sensors/index

  airflow/contrib/operators/index

  airflow/contrib/sensors/index


Hooks
-----
Hooks are interfaces to external platforms and databases, implementing a common
interface when possible and acting as building blocks for operators. All hooks
are derived from :class:`~airflow.hooks.base_hook.BaseHook`.

Hooks packages
''''''''''''''
All hooks are in the following packages:

.. toctree::
  :includehidden:
  :glob:
  :maxdepth: 1

  airflow/hooks/index

  airflow/contrib/hooks/index


Executors
---------
Executors are the mechanism by which task instances get run. All executors are
derived from :class:`~airflow.executors.base_executor.BaseExecutor`.

Executors packages
''''''''''''''''''
All executors are in the following packages:

.. toctree::
  :includehidden:
  :glob:
  :maxdepth: 1

  airflow/executors/index

  airflow/contrib/executors/index


Models
------
Models are built on top of the SQLAlchemy ORM Base class, and instances are
persisted in the database.

.. toctree::
  :includehidden:
  :glob:
  :maxdepth: 1

  airflow/models/index


Core and community package
--------------------------
Formerly the core code was maintained by the original creators - Airbnb. The code
that was in the contrib package was supported by the community. The project
was passed to the Apache community and currently the entire code is
maintained by the community, so now the division has no justification,
and it is only due to historical reasons. Currently, all new classes are
added only to the contrib package.